WASHINGTON -- A video by Islamic State militants Tuesday purported to show the cold-blooded execution of American journalist James Foley as retribution for U.S. airstrikes in Iraq. The White House, his family and employer said they could not determine the video's authenticity and were attempting to confirm if he had been killed.

Foley, a 40-year-old freelance journalist from Rochester, New Hampshire, went missing nearly two years ago in northern Syria while on assignment for Agence France-Press and the Boston-based media company GlobalPost. The car he was riding in was stopped by four militants in a contested battle zone that both Sunni rebel fighters and government forces were trying to control. He had not been heard from since.

White House National Security Council spokeswoman Caitlin Hayden said the administration has seen the video and that the intelligence community is working as quickly as possible to determine if it is authentic.

"If genuine, we are appalled by the brutal murder of an innocent American journalist and we express our deepest condolences to his family and friends," Hayden said in a statement.

Philip Balboni, GlobalPost CEO and co-founder, said the company had been informed that the FBI is in the process of evaluating the video to determine whether it was authentic. "We ask for your prayers for Jim and his family," he said.

Several senior U.S. officials with direct knowledge of the situation said the Islamic State very recently threatened to kill Foley to avenge the crushing airstrikes over the last two weeks against militants advancing on Mount Sinjar, the Mosul dam and the Kurdish capital of Irbil.

Both areas are in northern Iraq, which has become a key front for the Islamic State as its fighters travel to and from Syria.

The officials spoke on condition of anonymity because they were not authorized to discuss the hostage situation by name.

Since Aug. 8, the U.S. military has struck more than 70 Islamic State targets -- including security checkpoints, vehicles and weapons caches. It's not clear how many militants have been killed in the strikes, although it's likely that some were.

The Islamic State militant group is so ruthless in its attacks against all people they consider heretics or infidels that it has been disowned by al-Qaida's leaders. In seeking to impose its harsh interpretation of Islamic law in the lands it is trying to control, the extremists have slain soldiers and civilians alike in horrifying executions -- including mounting the decapitated heads of some of its victims on spikes.

The group is the heir apparent of the militancy known as al-Qaida in Iraq, which beheaded many of its victims, including Americans businessman Nicholas Berg in 2004.